A diesel engine system generally comprises one or more combustion chambers, which are individually defined by a reciprocating piston inside a cylinder. The cylinder is provided with electrically controllable injection means for injecting fuel inside the combustion chamber. The cylinder is also provided with one or more intake valves for cyclically opening the combustion chamber towards an intake line for receiving fresh airflow, and with one or more exhaust valves for cyclically opening the combustion chamber towards an exhaust line for discharging the exhaust gases.
The exhaust line comprises a diesel oxidation catalyst (DOC) which is conventionally provided for reducing the toxicity of emissions from diesel engine. In order to accomplish tighter emission legislation, most of the diesel engine systems are also equipped with a diesel particulate filter (DPF), which is located in the exhaust line downstream the DOC for capturing and removing diesel particulate matter (soot) from the exhaust gas flow.
The diesel oxidation catalyst (DOC) is especially provided for oxidizing hydrocarbons (HC) and carbon monoxides (CO), which are formed in the combustion process of the engine and are contained in the exhaust gas flow. More particularly, the diesel oxidation catalyst uses excess oxygen (O2) in the exhaust gas flow for oxidizing carbon monoxide to carbon dioxide (CO2), and for oxidizing hydrocarbons to water (H2O) and carbon dioxide (CO2). Such oxidations are exothermic reactions, which increase the catalyst temperature as well as the temperature of the exhaust gas flow downstream the catalyst.
The total heat rate within an active diesel particulate catalyst is determined by two main factors. The first main factor is represented by the heat exchange rate, which is related to the conventional processes between exhaust gases, diesel oxidation catalyst, and environment. The second main factor is represented by the oxidation heat release rate, which is related to the exothermic oxidation reactions into the diesel oxidation catalyst. This second main factor is a key parameter in establishing the diesel oxidation catalyst efficiency.
During its operative life, diesel oxidation catalysts gradually reduce their efficiency. Modern diesel engine systems are provided with a diagnostic system suitable for determining an efficiency index of the diesel oxidation catalyst. Such diagnostic system generally comprise two sensors for measuring the exhaust gas temperature upstream and downstream the diesel oxidation catalyst.
A microprocessor-based controller applies said temperature measures to a computer code for calculating the actual oxidation heat release rate, which is related to the exothermic oxidation reactions in the diesel oxidation catalyst. The controller further comprises a computer code for implementing a physical model of the diesel oxidation catalyst, by means of which the oxidation heat release rate is estimated as a function of the exhaust gas temperature upstream the catalyst. Such a model is calibrated on a fresh diesel oxidation catalyst, in order to estimate the nominal oxidation heat release rate, which is theoretically produced by a new catalyst.
The efficiency index is then calculated dividing the actual (measured) heat release rate by the estimated (nominal) heat release oxidation rate. In fact, such efficiency index establishes the rate at which the exothermic reactions occur in the diesel oxidation catalyst as expected by a fresh catalyst. Therefore, when the efficiency index is below a certain threshold, the diagnostic system warns that the diesel oxidation catalyst is faulty and must be replaced.
A drawback of the above-mentioned diagnostic device is that the effectiveness of the index is strongly dependent on the DOC physical model error. Another drawback is that such a physical model is generally very complex, so that it is difficult to calibrate and requires a powerful hardware to be implemented.
Accordingly, at least one aim is to solve, or at least to positively reduce, the above-mentioned drawbacks with a simple, rational and inexpensive solution. In addition, other aims, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.